Re: [PATCH] xfs: restore bi_bdev in xfs_zone_gc_write_chunk

On Thu, Aug 13, 2026 at 04:56:12PM +0200, Christoph Hellwig wrote:
> xfs_zone_gc_write_chunk relies on bi_bdev to still be valid, which is not
> true when XFS is used on top of a stacked block device.  This can lead to
> misdirected GC writes, writing of plain text when using dm-crypt, or
> miscalculated I/O limits in xfs_zone_gc_split_write.
> 
> Fix this by reassigning bi_bdev.

ewww, what??

Should bio_reuse take a bdev parameter and set_dev itself?  I had no
idea that bi_bdev could get changed by the time the bio completes.

> Fixes: 080d01c41d44 ("xfs: implement zoned garbage collection")
> Signed-off-by: Christoph Hellwig <[email protected]>

From a purely defensive standpoint this makes sense, so

Cc: <[email protected]> # v6.15
Reviewed-by: "Darrick J. Wong" <[email protected]>

--D

> ---
>  fs/xfs/xfs_zone_gc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
> index 7ab8f2218c6a..5cc5ad1e3483 100644
> --- a/fs/xfs/xfs_zone_gc.c
> +++ b/fs/xfs/xfs_zone_gc.c
> @@ -869,6 +869,11 @@ xfs_zone_gc_write_chunk(
>  	WRITE_ONCE(chunk->state, XFS_GC_BIO_NEW);
>  	list_move_tail(&chunk->entry, &data->writing);
>  
> +	/*
> +	 * If we run on top of stacked block device, the read I/O might have
> +	 * reset bi_bdev, restore it to the one we want.
> +	 */
> +	bio_set_dev(&chunk->bio, mp->m_rtdev_targp->bt_bdev);
>  	bio_reuse(&chunk->bio, REQ_OP_WRITE);
>  	while ((split_chunk = xfs_zone_gc_split_write(data, chunk)))
>  		xfs_zone_gc_submit_write(data, split_chunk);
> -- 
> 2.53.0
> 
>